<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>div to img demo</title>
	<style type="text/css">
		.content{
			display: block;

			position: relative;

			width: 300px;
			height: 300px;

			background-color: #E6B246
		}
	</style>
</head>
<body>
	<div class="content" id="imgDiv">
		<div>测试</div>
	</div>
	<button id="btn">保存为图片</button>
</body>
</html>
<script src="js/jquery-1.8.2.js"></script>
<script src="js/bluebird.js"></script>
<script src="js/html2canvas.min.js"></script>
<script type="text/javascript">
$(document).ready(function(){
	// canvas生成图片
        $("#btn").on("click", function () {
            var getPixelRatio = function (context) { // 获取设备的PixelRatio
                var backingStore = context.backingStorePixelRatio ||
                    context.webkitBackingStorePixelRatio ||
                    context.mozBackingStorePixelRatio ||
                    context.msBackingStorePixelRatio ||
                    context.oBackingStorePixelRatio ||
                    context.backingStorePixelRatio || 0.5;
                return (window.devicePixelRatio || 0.5) / backingStore;
            };
            //生成的图片名称
            var imgName = "cs.jpg";
            var shareContent = document.getElementById("imgDiv");
            var width = shareContent.offsetWidth;
            var height = shareContent.offsetHeight;
            var canvas = document.createElement("canvas");
            var context = canvas.getContext('2d');
            var scale = getPixelRatio(context); //将canvas的容器扩大PixelRatio倍，再将画布缩放，将图像放大PixelRatio倍。
            canvas.width = width * scale;
            canvas.height = height * scale;
            canvas.style.width = width + 'px';
            canvas.style.height = height + 'px';
            context.scale(scale, scale);

            var opts = {
                scale: scale,
                canvas: canvas,
                width: width,
                height: height,
                dpi: window.devicePixelRatio
            };
            html2canvas(shareContent, opts).then(function (canvas) {
                context.imageSmoothingEnabled = false;
                context.webkitImageSmoothingEnabled = false;
                context.msImageSmoothingEnabled = false;
                context.imageSmoothingEnabled = false;
                var dataUrl = canvas.toDataURL('image/jpeg', 1.0);
                dataURIToBlob(imgName, dataUrl, callback);
            });
        });
})
	

        // edited from https://developer.mozilla.org/en-US/docs/Web/API/HTMLCanvasElement/toBlob#Polyfill
       var dataURIToBlob =  function (imgName, dataURI, callback) {
            var binStr = atob(dataURI.split(',')[1]),
                len = binStr.length,
                arr = new Uint8Array(len);

            for (var i = 0; i < len; i++) {
                arr[i] = binStr.charCodeAt(i);
            }

            callback(imgName, new Blob([arr]));
        }

        var callback = function (imgName, blob) {
            var triggerDownload = $("<a>").attr("href", URL.createObjectURL(blob)).attr("download", imgName).appendTo("body").on("click", function () {
                if (navigator.msSaveBlob) {
                    return navigator.msSaveBlob(blob, imgName);
                }
            });
            triggerDownload[0].click();
            triggerDownload.remove();
        };
</script>